If one gets a Nightly update but does not restart and rather dismisses
the notification, the next update check will do the update again.

This is caused by the fact that the version check is done based on
semver, but Nightly has the very same version that differs by the SHA
only.
Adjust the Nightly update check to skip re-downloads if SHA parts of the
version match also.

https://github.com/zed-industries/zed/pull/59852 does more changes, this
PR extracts the part I am sure about.

Release Notes:

- N/A